Twice the height of the Empire State - massive solar tower for AZ | Hacker News Reader

Twice the height of the Empire State - massive solar tower for AZ

gizmag.com

192 pointsaditiyaa1127 comments

Really? Very cool idea, but some of the claims sound downright ridiculous.

First, the zero maintenance claim that is touted at least 3 times by the article seems suspicious. You can't really leave anything out in the desert sun and not have to maintain or replace it. Sun will disintegrate a lot of material, not to mention wind and sand. Anybody have any info or insight into what material they are using to create the "greenhouse"?

Additionally, the claim that "In fact, because you're creating a greenhouse underneath, it actually turns out to be remarkably good for growing vegetation under there." does not seem to jibe at all with the claimed temperatures ("add in the greenhouse effect and you've got a temperature under your collector somewhere around 80-90 degrees (176-194 F)"). I'm not sure I'm familiar with any vegetation that grows in near 200 degree temperatures.

Does anyone have any actual experience with this kind of tech?

Desert environments are extremely good at preserving things, particularly technological devices.

http://maps.google.com/maps?q=Mojave,+CA&hl=en&ll=35...

The above link shows an aircraft storage facility in Mojave, California. There are a number of such facilities in the US, and many more worldwide. It was discovered some decades ago that you can leave a plane in the desert for years at a time, and when you come back to it there's very little maintenance that has to be done to make them airworthy again.

There was a story that I read a few months ago that I sadly can't find a link to at the moment. Some years back during one war or another, there was a plane that had engine problems. If I remember correctly, this was in northern Africa. The crew radioed that they were coming back to base, but they never made it. They were flying over a desert area.

A lot of years went by, and some prospectors working for an oil company were driving around the desert looking for places to drill and they came across the wreck of the plane.

The tail of the plane had broken off during the crash, but otherwise the plane was in excellent condition. There was still fuel in the tanks and the batteries were still charged. The oil guys were even able to turn on the lights and get the engines to turn over (might be wrong about that, but I think I remember that). If the tail hadn't broken, they likely could have been able to fly it out of there with not so much work.

So anyway, putting stuff in the desert isn't no maintenance, but it is low maintenance.

I do agree with your assessment about the greenhouse. Deserts are already pretty hot and plants don't grow well there. I don't think 2-3x the temp will be a big improvement.

I'm pretty sure that was part of the plot from The Mummy? :)

In any case, desert is great for preserving stuff in terms of low humidity (ie things don't rot). Not so good for preserving stuff in terms of them getting sand blasted. Especially in AZ where winds routinely hit 100mph+ during gusts and 60mph during windstorms. Not to mention the haboobs.

Also, the prototype of this tower in Spain figured out that the plastics they were using were "not durable enough". I would imagine that means they disintegrated? I'm wondering what they're planning on building this thing out of.

http://en.wikipedia.org/wiki/Solar_updraft_tower#First_Proto...

  > I'm pretty sure that was part of the plot
  > from The Mummy? :)

http://en.wikipedia.org/wiki/Lady_Be_Good_(aircraft)

Ah thanks! Flight of the Phoenix was the movie I was thinking of.

Hey geuis,

I'm the guy who submitted that story ;)

It was in Libya during WWII that it happened:

http://news.ycombinator.com/item?id=2475048

Awesome! Thanks

The Italisn S79, lost in Libya desert during Ww II and found many years later during some petrol research. Article in italian: http://www.locotoco.altervista.org/Viaggi/libia_1997-98/s79....

Seems to me like you'd need to keep all the glass clean too, which means more manpower & water/air power to get all the crap off.

I'd be quite curious what the actual maintenance costs will be. Still, no feedstock into the process means that you'd have to have pretty serious component failure to bring the running costs up to oil plants presumably.

Yes, but that brings up a good question. Anyone who owns a computer knows that air isn't pristine. It picks up all kinds of crap. If this beast has as much suction as the article implies, it's going to be inhaling all kinds of debris. I would guess it gets filtered so you don't damage the turbines, in which case somebody's going to have to be cleaning those filters pretty regularly.

That's a good point. Let me clarify. They won't have to pay for a feedstock. They may have to pay to ensure that there isn't damage to turbines, but i would have to think that turbines would be sturdy enough to cope w/ some particulate matter (or that wear and tear would be factored into maintenance costs).

What i'd also be interested in hearing is whether there's a drop in efficiency if particulate matter increases, and if so, what kind of curve fits the inefficiency

The turbines will basically be the same as wind turbines rather than the steam/gas turbine you might be thinking of. They won't be bothered by dust.

If I had that much glass to clean I'd certainly have robots doing it.

I'm trying to figure out how they would keep enough moisture in the "greenhouse." By definition there's a breeze so it's like using an air dryer on your garden - you would need to provide a lot of water to keep the plants and soil moist. That water has to come from somewhere. In addition, evaporative cooling reduces the amount of power the facility will generate and makes it heavier to lift out. Although the density of the air going through the turbines might compensate.

Yeah, no way plants are going to survive in 180 degree heat with constant breeze wicking away moisture.

This will be an interesting project. Having lived in Las Vegas for a few years I can certainly see how they expect it to work. However planting grass inside the greenhouse seems a bit much.

The plant will be limited by how much heat can be put into the air inside the 'greenhouse' and overall it will be interesting to see how the feed in replacement cool air without creating dust storms and sucking up birds and what not. I don't suppose someone with Mathematica can build up the spreadsheet using the perfect gas law and the air convection to see if their claims are close. 200MW is 200 sq kilometers of surface area at a nominal solar insolation of 1KW/meter but with an efficency of 10 - 15% and an actual insolation in AZ nearer 800W/m2 that is 1.6M sq kilometers of surface area for 15% conversion rate.

I'm wondering if they have the math they did posted somewhere.

Your calculations are out by several orders of magnitude (don't forget that 1 km^2 = 1,000,000 m^2).

200MW at 10% efficiency and 800W/m insolation is 2.5 km^2 (I believe their claimed efficiency is considerably lower than that, though).

For what it's worth, the article doesn't claim "zero maintenance"— in fact it explicitly says "apart from a bit of turbine servicing now and then."

Now whether that's still a wildly optimistic claim is up for grabs.

When jibe is used to mean "agree", jibe jibes jibe.

    The Arizona tower will be a staggering 800 metres or so tall - just 30 meters
    shorter than the colossal Burj Khalifa in Dubai, the world's tallest
    man-made structure.

Is there any reason why this can't be constructed to be 831 meters tall to edge out the Burj Dubai?

I think that Burj Khalifa (formerly known as Burj Dubai) should be the tallest for economic reasons. The Arizona tower is simply infrastructure, so its goals are to produce the most energy for the least cost. Adding 31 meters may upset the cost/benefit ratio. Dubai, on the other hand, is a tourist destination, and having the tallest building in the world is good marketing.

I'm willing to bet Burj Khalifa wasn't built tallest for purely economic reasons. I have a suspicion ego was at least a tiny factor.

and then that ego was bruised when they had to change the name to the guy who runs the city next door because he bailed you out

But... 'merica.

... fuck yeah!

Honestly though, why compete just to show off? There its making money as the tallest structure, here it will be completely isolated, nobody comes here, whoopteedoo.

Here it is also all about cost-benefit. There will be no tourism.

There will be no tourism.

I'd want to see it if I am in Arizona! But I don't care if it is tallest structure in the world, I'm in it for the power engineering.

me too! did you notice what looked like a "viewing ring" at the top of the tower in the video? i wonder what all the wind sounds like up there, and if birds will circle it all day, etc.

By 2015, there will probably be three or four other buildings taller than the Burj.

Because "who has the longest" contests are... well, stupid.

Seriously, why would you build the tower higher than needed, only to "edge out" some empty building in the Arabian desert? Aren't there... sorry "ain't there" more important things?

It's pretty unlikely, but fun to think that they might be planning on pulling something similar to the Chrysler Building.

http://en.wikipedia.org/wiki/Chrysler_Building#Construction

Because, the building in Dubai will grow to 832 meters once they're done.

For any other Aussies that, like me, vaguely remember the plans for building this near Mildura but can't be bothered watching the video to find out why it didn't happen, the reason cited is a "complete lack of incentives".

Sad that something like this couldn't get a dime from the Australian government while the US "welcomed them with open arms" (and, presumably, truckloads of cash).

That's not a good sign. I mean, ideally, you'd want the incentive to be, "It produces power cheaper than coal!"

Presumably it could if you factor in coal's carbon externalities.

What makes you think that?

Not sure why I can't edit my post. Anyway - downvoted for asking for clarification on an unsupported assertion. HN at its most scientifically rigorous!

Building a new plant is always going to be more expensive than just digging out some more coal and burning it in an existing facility.

Also - we have lots of coal.

The trouble is no one's ever built anything like this yet, so it's still risky. That's part of why we need government incentives. Once we know it works the incentives won't be necessary, the market will be happy to finance more of them.

I love this technology a whole lot, but this is Hacker News so it is worthwhile to think critically about this kind of "press release"-style news posting. This article does a bit of hand waving with the numbers, and, while this is an amazingly cool project, I think that they are overselling its benefits.

First, let's get the terminology right. This plant has a capacity of 200 MW. That does not mean that it produces 200 MWh. The formula for converting MW into (annual) MWh is the following:

MWh = MWx365x24xCF

In the above formula, CF is the capacity factor. Capacity factor is basically the amount of energy that a plant is actually able to produce over the course of a year divided by the total capacity of the plant. Here are some common capacity factors for various industries (taken from a private document, so no sources but this stuff is easy enough to google):

* Coal - 65-95%

* Natural Gas - 35-65%

* Hydro - 25-65%

* Solar - 20-35%

* Wind - 20-35%

* Nuclear - 80%+

Capacity factors are never 100% for various reasons:

* Plants may need to be taken offline for refueling, maintenance, or inspection

* For renewables, the wind isn't always going at full speed and the sun isn't always shining

* A whole bunch of other things that I am too tired to list (read the references below, they have some more in them)

Now, let's look at this new project, and one of the claims made in this article.

According to the article, this plant will be able to provide power for 150,000 homes. According to the EIA, the average household annual energy usage is 10,896 KWh. Given this information and using a more generous solar capacity factor (35%):

Number of Homes Powered = (200x365x24x.35) / 10.896 = 56,278 homes

Hmm, well that's just a bit less than what the article claimed, so they must be assuming a really amazing capacity factor for this estimate. Let's solve the below for cf and see what we get....

(200x365x24xcf)/10.896=150000

cf = approx. 93%

Look, I'm all for scientific advancement and alternative energy, but can we try to be more sensible than this? This is a highly improbable capacity factor.

Documents available from Enviro Mission says that the simulated capacity factor will be more like 50%. When we plug that number into the equation we get about 80,397 homes, which is pretty sensible. However, we have to remember that these are only simulated numbers. There are no similar projects currently available that can be compared to this one, so the actual capacity factor may be either more or less.

Note: Please keep in mind that efficiency is a totally different concept from capacity factor. Efficiency is typically used to describe how well a plant transfers from its energy source into electricity^. The capacity of a plant is a number that already incorporates the plant's efficiency. The capacity factor is simply a measure of how much of that capacity is actually used on an annual basis on average.

^ I am not an electrical engineer. I am an economist, that is the best definition I can come up with.

Disclaimer: I am incredibly tired right now, so if any errors appear in the above posting please send me some coffee so that I can correct them before falling asleep.

References:

+ http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3

+ http://www.solarpaces.org/CSP_Technology/docs/solar_tower.pd...

+ http://www.enviromission.com.au/IRM/Company/ShowPage.aspx?CP...

Edit: Formatting was all messed up the first time. Forgot to include some additional information. Added clarification on efficiency.

Appreciate the analysis, however I believe you made a fairly significant error with the solar capacity percentage. Unlike other solar power, the cool thing about this structure is that it doesn't specifically require constant sunshine to work effectively being that it works off the temperature differential through the tower, rather than pulling energy strictly from solar panels. Because of this, I would imagine capacity to be much nearer to 100% than the opposite.

"for every hundred metres you go up from the surface, the ambient temperature drops by about 1 degree. The greater the temperature differential, the harder the tower sucks up that hot air at the bottom - and the more energy you can generate through the turbines... Because the heat of the day warms the ground up so much, it continues working at night;"

As for how the difference in temperature between the surface and 100s of meters in the air changes throughout the day/night, I don't know.

So according to your equation, at 80% capacity, it could cover 128k homes. At 93.3% capacity it'd reach 150k.

It still needs a temperature differential to run, which will not be there at night, so the best you could get is about 50%. This is the number that Enviro Mission uses.

The article claims, "Because the heat of the day warms the ground up so much, it continues working at night"

It also means less power generation in the morning. The thermal inertia in the base means it lags behind the air temperature, so there will be times when the base and top are the same temperature.

Not necessarily. Lets say the lows at the top of the tower are maybe 40 degrees F. They're heating up the base to 180 degrees F during the heat of the day. Whether the thermal gradient ever inverts depends on whether the ambient nighttime temperatures are able to bring that 180 degree thermal mass (concrete? dirt?) down to 40 degrees in the time available before the sun comes back up. You'd have to do the math.

What you say is correct. If there's energy production at night using stored heat then it's pulling out power from the heat reserve and cooling it down. If, say, the system was 10% efficient at producing power directly and put 25% into heat reserves which are 80% efficient at releasing that heat and turing it into power, then yes, the bottom would, excepting rare cases (strange weather?), be warmer than the top.

I don't believe that is the case for two hand-waving reasons. The desert in northern New Mexico (where I lived) gets a thermal inversions. You can see that smoke from morning fires rises, hits the inversion layer, and goes horizontal. I believe this is common in deserts, at least those with mountains. From http://www.srh.noaa.gov/media/abq/LocalStudies/ABQthermalinv... there's an 5.8C difference for shallow (~155m thick) inversions, which occurs throughout the year, and there were "130 inversion cases" in that year. Thus, the "1 degree per 100 meters" rule of thumb only applies during the day. A power system would have to work against the inversion.

Second, power extraction is more efficient with higher differentials. It would, I believe, be better to extract more power during the day (when the difference is high and demand for cooling is also high) than to store it for energy production at night.

The previous comment proposed the "capacity to be much nearer to 100% than the opposite." I just don't see that as being likely.

For working against the inversion, a simple solution would be to implement some venting along the sides and vent at the height of minimum temperature for a maximum differential, assuming that if the inversion was strong enough and the minimum temperature was lower in altitude than the max height of the tower. Yeah, you're gonna lose efficiency, but you'd still be able to generate some power, but I think even with that amount of thermal mass you could still maintain a decent differential I think. Also, southwestern and northeastern Arizona are pretty flat and the southwestern part is much much lower in altitude than Albuquerque.

Also, where from NM are you? I'm from ABQ and Farmington.

But there isn't much power there, and we aren't good at extracting power efficiently from lower temperature differentials. I read that wind power goes as the cube of the wind speed, so you really want to maximize this system to extract power during the day time (when the temperature difference and hence wind speed is most), and not the night. Even if it can support 1/2 the wind speed, that's only 1/8th of the power production.

Yeah, ABQ's in the valley so it's probably more prone to thermal inversions. I get the idea (eg, from http://www.arizonensis.org/news/sonorandesertedition/news03_... "PHOENIX, Az. ... The perfume is most noticeable after dark when temperature inversions trap it close to the ground.") that mountains aren't required, and that it's a common feature of deserts, but I wasn't able to track down numbers.

I was in Santa Fe for 8 years. I come back about once a year for my green chile fix. ;)

The most exciting claim to me was how efficient and robust this method of harnessing solar was. In particular:

- "Because it works on temperature differential, not absolute temperature, it works in any weather"

- "Because the heat of the day warms the ground up so much, it continues working at night"

- "It requires virtually no maintenance - apart from a bit of turbine servicing now and then, the tower "just works" once it's going, and lasts as long as its structure stays standing"

If these claims are true, then it would make sense for this plant to have a much higher capacity factor than most solar plants given that the major factors lowering CF is mitigated in this design (works at night and no shutdown for maintenance). Maybe I'm stuck in CS land where we think by factors of 10 but the numbers in this article doesn't seem too far off the beaten path.

IMO the most significant oversight efficiency of around 60% figure which is ridiculously high. Solar towers are vary low efficiency heat engines and have trouble reaching 1% efficiency (yes 1% efficiency ). The 38 km² collecting area is expected to extract about 0.5 percent, or 5 W/m² of 1 kW/m², of the solar power that falls upon it. http://en.wikipedia.org/wiki/Solar_updraft_tower

I read their use of the term "60% efficiency" as what would more correctly be described as a Capacity Factor, in the sense used by Spyro above.

Whether they can actually average 120MW in operation, I don't know.

They are not using solar panels, they are creating a giant heat pump. They are therefore relying on there being a heat differential between the top and bottom of the tower.

Greenhouse gets hot, creates a pressure difference between inside the greenhouse and outside of the tower at the top, air flows up through turbines. It is very simple.

There are very few moving parts and it is always going to be colder at the top of the tower than at the bottom.

Note that it isn't pure desert floor, but a man made structure that will purposefully trap heat. Imagine how hot it would get if you sat in your car with the windows rolled up in the middle of the desert. Then think about how cold it would be at 2x the height of the empire state building.

It will be colder just because of the air pressure at that altitude. Even so, the ground cools at a much different rate than air does, so I'm sure night time generation is bolstered somewhat by that.

It will have a very high capacity factor because the only thing that you should ever have to 'fix' is the turbine, which should last quite a long time.

It seems likely that cf will be much higher than even that of nuclear.

It might continue to generate during the night, but I would be very surprised if its nighttime capacity was even a quarter what it generated during the day. Also, the glass will need to be cleaned periodically.

From Enviro's Web site: "A single 200MW Solar Tower power station will provide enough electricity to power around 100,000 households, similar to the number of homes in a city the size of Burbank (California, USA) or Palm Bay (Florida, USA)."

They're saying, 100k, not the 150 from the article. That seems more realistic.

From the Phoenix Business Journal: " . . . air is funneled up the tower at 35 mph past 32 wind turbines at its base . . . " http://www.bizjournals.com/phoenix/print-edition/2010/10/29/... That's a pretty impressive air velocity.

Um, regarding "MWh = MWx365x24xCF", isn't an hour 3600 seconds, so isn't the factor 3600? You seem to be converting using days in year and hours in day, yielding a factor-of-ten error.

With the numbers supplied the calculation is correct. As written it is ambiguous though.

Think of it as: MWh/year = MWh/h x 365 x 24 x CF

I could be wrong, what why is it called a solar tower when it's mainly based on Bernoulli?

It's a regret that I'm late to the commenting party. This comment won't get seen, so I won't get any feedback.

However ...

I haven't been able to find out what the upflow airspeed will be. If it's large enough one could wear a winged suit and freefall in the funnel. That would be awesome.

This is just so cool. I'm curious about the local weather impact of something like this. Basically, what these guys are doing is creating a continuous, artificial thermal, the same type you use for flying hang gliders and sailplanes. I'm certain the guys have done the math, but I'm wondering if you won't get cloud formation above the tower due to condensation of the hot air rising through the tower.

Meteorological theory suggests that you would definitely get this if the airflow was not contained by the turbines, and cloud formation with the release of condensation heat would cause even more cloud formation which would basically result in a giant, permanent thundercloud above the power plant. This would obviously decrease insolation a lot.

Anyone in here who has done any theory on these kinds of projects? I'm just guessing based on my knowledge of gliding that a considerable amount of the energy collected from this power plant actually comes from the temperature differential between not just the solar energy collected directly underneath the tower. It isn't just the fact that hot air rises. Due to decreasing pressure, the air temperature of a mass of air decreases approximately one degree per hundred meters of altitude gained. But if the atmospheric temperature distribution due to meteorological conditions is such that the actual temperature in the atmosphere drops _more_ than one degree per hundred meters of altitude, you have an untapped energy source; any air mass set in motion upwards will actually accelerate instead of slowing down.

That we are making large-scale technology to exploit this is so ridiculously cool I have problems expressing it.

It's a desert. The air near the ground is usually pretty dry. That's why radiation cooling makes things cool off so much at night (instead of making clouds and fog).

Big toy.

For one, maintenance will _not_ be low. Wind turbines (and nothing else is used here) do have quite some maintenance costs, and additionally, you need to keep the greenhouse clean.

The main problem I see is the capacity. 200 MW peak capacity at 60% efficiency translates to 120 MW peak electric energy. If we assume 50% capacity factor (which I suspect is _very_ generous), we arrive at 60 MWe average output. You would need 15 of these to substitute for a single 1 GW nuclear plant.

Big toy.

Wish I could downvote your post for repetition and for just making up stuff.

'200 MW peak capacity at 60% efficiency translates to 120 MW peak electric energy'. This sentence makes no sense. They are building a 200MW plant. That is the amount of electricity it will put out at peak.

You made up the number for 50% capacity figure just then didn't you? You did. I just saw you. So your final figure is wrong.

I agree the 200MW is output, so no efficient factor should be added, but Enviromission says the capacity factor is 50%:

http://www.enviromission.com.au/IRM/Company/ShowPage.aspx?CP...

Makes sense, since half of the time it's night...

Absolutely correct. Thanks for that link.

The 50% capacity figure is from their own website, but I still suspect it to be too generous.

My reason for assuming that the "200" is not the electrical net output is that they write "MW", not "MWe". I have become quite cynical about the numbers on nameplates; they simply stick the biggest number on the thing that somehow appears in the calculation. Maybe I am wrong, and that is actually the peak electrical output.

However, that peak is only reached at noon in june. So, perhaps the actual yearly average output is 80 MW. Perhaps it is even 100 MW. It is still a big toy, and an expensive one at that.

60%? Darn. I was hoping for better after the hype earlier in the article. Don't large steam plants approach 99%?

150,000 US Homes

Is that a lot? I hate to (continue to) be a cynic, but it doesn't sound like a lot.

The Census says there are 110,692,000 occupied homes in the US, so 150k is 0.136% of that.[1] That means that there would need to be 738 of them to meet demand.

Now, the EIA says there are about 5700 power plants currently operating in the US [2]. Continuing with the back of the envelope math, that's almost 8 times as many as would be necessary if they all produced as much as this one. Pick whatever factor you want for "non-home" energy, but we're dealing with the right order of magnitude.

Combine that with the clean energy aspect of it, and I don't see a lot of reason to be cynical.

[1] http://www.census.gov/hhes/www/housing/ahs/ahsfaq.html [2] http://www.eia.gov/tools/faqs/faq.cfm?id=65&t=2

The other aspect you're missing is the probably somewhat larger energy consumption from non-residential properties.

Wikipedia [1] says that the energy consumption of the US is 25,000 TWh per annum. Looking at the top rated comment and picking instead a CF between the two (I used 0.6); we're looking at this tower producing in the region of 1TWh.

So you'd actually need about 25,000 of these towers to provide for the energy requirements of the US. Ouch.

Edit: obviously, this is for the complete replacement of all existing energy use with clean renewable electricity. The gross US electricity production is given [2] as 4344 TWh (2008).

[1] http://en.wikipedia.org/wiki/Energy_in_the_United_States [2] http://en.wikipedia.org/wiki/Electricity_sector_of_the_Unite...

So at $750 million a pop, that's a little over $550 billion to power US homes. Or, roughly 50% of the annual budget of the military to power all US homes for 80 years!

Clearly back of the envelope numbers, but definitely something to be excited about.

Well, you can't only have these things powering US homes because I can't imagine they work that well at night.

They do actually.

Truth be told, the article doesn't say how well they work at night. I don't think that it'll work just as good, but that doesn't mean it won't work at all.

99%? No. The Carnot limit is much lower than that for the temperatures at which steam turbines operate.

Besides, the thermodynamic efficiency isn't particularly relevant for technologies like this anyway - you're not paying for the input, after all. The efficiencies you care about here are watt/area, energy payback time and, ultimately, $/watt.

thermodynamic efficiency should correlate pretty strongly to watt/area because the device harvests sunlight.

For this technology, but not for the competitors that you'd want to compare them with.

60% was a plant factor, meaning that the 200 MW plant output will be 200 * .6 when averaged over the course of a year, presumably because some turbines will be down for maintenance some of the time, and the temperature difference will be less at times, so it can't always put out maximum power.

And there will be transmission line outages some times too.

60% has nothing to do with the efficiency of the transfer of energy.

He says in the video coal plants run 80% plant factor, nuclear plants would be even higher, probably putting out over 90% of their rated power.

It claims 200MW/150,000 homes = 1.3KW for a US home !!!! So homes in Arizona don't have AC or electrical appliances and are all owned by eco-warriors

the top comment right now has a reference to the EIA which states that the average homes uses 10,896 KWh in a year. divide by 8,760 and you get 1.24 KW average

all of the appliances are not on all the time, sometimes more power is used, sometimes less. 1.3 kw per hour for every hour in the year is the average.

Checked the figures and 1.3Kw is the average (24*365) for Arizona.

Surprising - when I lived in Houston you needed AC running 24x7 for 6months of the year and all the other appliances where electric.

I assume, being in the desert, Arizona is cooler at night and they use propane/oil heating in the winter?

I don't see it mentioned in the article, but the greenhouse must be colossal. These updraft towers use land far less efficiently than concentrated solar and those don't use land efficiently either.

From http://en.wikipedia.org/wiki/Solar_updraft_tower

A 200 MW power plant with the same 1000-metre-high tower would need a collector 7 kilometres in diameter (total area of about 38 km²). The 38 km² collecting area is expected to extract about 0.5 percent, or 5 W/m² of 1 kW/m², of the solar power that falls upon it. Note that in comparison, concentrating thermal (CSP) or photovoltaic (CPV) solar power plants have an efficiency ranging between 20% to 31.25%

38 square kilometers, these things don't make sense if you don't use the greenhouse for something. Hopefully the wiki is outdated and they have a higher efficiency.

When you have an almost comedic overabundance of uninhabited desert, a less efficient but cheaper technology may prove more economically effective. If, one day, the costs of more efficient technologies fall, or if suitable land becomes scarce, then efficiency will become a greater concern.

The whole point of these renewable energy projects is to be considerate to the environment. Covering up the desert, inhabited by tons of species (this is not the Sahara) in a greenhouse is an environmental disaster in a new skin.

Land use efficiency is a concern now for the environment. If renewable technologies have to cover up 60,000+ square miles of land not inhabited by humans, then coal and nuclear are the environmentally friendlier options.

From a strictly pragmatic perspective, I would argue that the loss of some desert habitat in an ecosystem that is not significantly linked with those used by humans for habitation, carbon sequestration, or agriculture is acceptable compared to the damage to higher-value ecosystems caused by air pollution from coal power. This assumes that environmental damage that causes long-term consequences for humans is considered more egregious than environmental damage that has no negative consequences for humans.

Personally, I think a thorium nuclear power plant in an isolated desert is a much more environmentally preferable approach than most renewable power sources.

It's better to make coal powerplants run cleaner too. Thorium will require serious effort to develop, a decade perhaps, but sure would be nice to have. Modern uranium is not that bad either.

There was some solar thermal project in California that ran into a lot of problems trying to use the desert land. Old power companies are paying environmental groups to protest those sprawling projects. Divide and conquer those hippies!

High altitude wind is the best source of renewable energy. It's concentrated and takes up airspace instead of land. They're taking their time though.

I see two insurmountable problems with this solar tower, in this age of rising environmental concerns and increasing influence of environmental pressure groups:

- The base of the tower covers a huge piece of land, which is now home to various desert creatures. Changing their habitat is unacceptable from the environmental protectionists' viewpoint. The precious creatures (probably some endangered species too) would probably die.

- Visual pollution. Nobody wants to have ugly structures in his backyard, let alone a half-a-mile-high tower which will be visible from a huge area. It detonates with the natural desert views of Arizona.

Because of these two reasons, this solar tower project will face years of litigation from environmental pressure groups, and in the end the project will probably stall.

On the other hand, this is probably precisely why this is being built in Arizona and not in California.

I agree.

You think environmentalists care more about "visual pollution", aka, "not in my back yard", than coal pollution, hydro dam flooding, nuclear meltdowns... I think maybe these people you are referring to aren't environmentalists at all.

It's planned for an extremely remote portion of the country. As of the 2010 census, the population density of La Paz county was 4 per square mile. It's quite possible that only a handful of people could end up seeing the thing.

If anyone was curious about the funding for this (I was), EnviroMission has a press release on their site [1]. "The Southern California Public Power Authority (SCPPA) has taken a call option to purchase the first of two EnviroMission 200MW Solar Tower power stations planned for development in La Paz County, Arizona." It does seem odd, though, that they are building these in Arizona when California has its own deserts.

[1] http://www.enviromission.com.au/EVM/Company/ShowPage.aspx/PD...

If I were to guess, the regulatory burden of putting something up like this in Arizona is probably way lower than putting it up in California. So, not that odd given that both sides are plugged into the grid and California already buys power from far away (like the Pacific NW.)

Even if this type of project only provides a small fraction of the energy we need, it is great to see funding and construction because experience building systems like the one in the article will lead to more effective systems in the future.

My wife and I live in Arizona (in the mountains) and we are having solar panels installed on our roof in 2 weeks that will furnish 100% or more of our electricity needs for about 10 months a year (and we will often make a little money back selling back power to our utility company) and cover about 50% of our needs the two months a year that we run our air conditioning.

A few friends have been critical of our decision for monetary reasons, and they may be right, but it is something we wanted to do. Also, if prices for energy, food, etc. increase dramatically, then we will break even on costs sooner rather than the anticipated 6 or 7 year time frame.

Wonderful if it works as described! That's quite a bit of power. I'd be very interested to know comparisons in terms of how long a traditional power plant takes to become profitable, and also how much initial investment this project is requiring.

750 million, payback in 11 years.

for comparison, hydro electric costs about $2 million per megawatt so a 200MW hydro plant would be $400 million, but with associated environmental concerns.

You mean they're actually going through with it? Awesome! I hope it works as well as planned.

I'm extremely interested in the aftermath of all this. The building itself is clever and all, but what will the ecological impact be? Wind farms kill birds and bats and there's evidence the sound drives many more off, concentrated solar has a nasty habit of significantly heating the air around the plant and hydro-dams are enormously destructive no matter how you look at it. What's a 1/2-mile-tall heat pump going to do?

Since this seems to work on temperature differentials, could you run it up the side of a mountain? Seems you could get height differences of 5-7k feet in a lot of places with that approach...

If you check out the wiki article then you can see that you are absolutely correct. You can get a system like this working on a mountainside as long as it faces the sun. I think there are some engineering tradeoffs that have to be considered and also environmental concerns. I think it's a lot easier to find a desert with minimal ecosystem compared to a mountainside

unless you had a perfectly vertical mountain your tower would end up being longer and costing more. if you did have a perfectly vertical mountain it would still be somewhat difficult to build on the side of a cliff.

I suppose you'd need a mountain in the desert as well.

The mountain would also provide unwanted shade.

Not necessarily. Depends on directional facing. A south facing spur up the mountain may provide no shade at all to the base.

And longer, yes, but not in need of vertical support.

This is a question out of pure curiosity, I'm not very well read on these subjects, so please forgive me if this is a dumb one.

Is there any reason why this can't be built as an underground structure? If it's working on temperature differentials, shouldn't you be able to achieve a more constant capacity by plugging it into earth where temperatures change less?

The sun doesn't shine underground...

But it shines on the ground, so instead of putting the heat source at the bottom of the cylinder, you put it on top and see temperatures drop as you go further down underground.

The article insists on the plant's low maintenance costs, so this may be a stupid question, but won't the greenhouse* have to be washed regularly of dust? I imagine the accumulation of detritus would significantly impact power production.

Edit: I previously had written mirrors. The concept art looked misleadingly shiny.

Compared to the cost of buying coal or natural gas and keeping all the machinery that moves and burns that clean, cleaning out the dust and debris this building takes in should cost relatively little.

if you think about the temperatures and pressures inside of modern combined cycle gas fired power plants, they need an exceptional amount of maintenance and repair. i'm sure the dirt loading is going to be a problem for these guys, but nowhere near the complexity and cost of super heated steam lines and huge boilers.

I wonder what effect this could have on the local climate. Pumping out hot air into cool air at height of 800 metres has got to have some affect.

Now if the base is used area is used for growing plants then the air emitted at the top would be moist, which I imagine would cause cloud formation as it meets the cold air.

I'm having lots of thoughts about climates within the rings.

I'd expect the temperature ranges to change at different distances frmo the centre. It may be that you could do agriculture at some points underneath.

On the other hand, it's likely that for best efficiency they'll need to create as much momentum as possible from the device.

But - the venturi effect will be significant underneath and they might need to shape the land in sections under the rings. Is it possible you could hide crops within glass casings that improve that effect?

Will water vapour collect at any point in particular?

I'm considering a science fiction plot based around people who live in housing built around energy towers like this.

When this is built, I'd be interested to do a roadtrip to see it.

This brings up an interesting possibility. What's stopping us from engineering these towers on to buildings once the technology is proven?

The huge area of glass enclosed space that needs to spread out from around the tower.

I've been following Enviromission for quite a while now (maybe since 2001?). I check out their website once a year or so to see how they are going. They have been championing this technology for quite a while.

I think it's sad that there are so many people doing back of the envelope calculations and wasting time typing them into Hacker News. There are 100s of millions of dollars involved people. Someone qualified will check the figures. And really it's not rocket science.

I think it's sad that you think that. One of the fundamental qualities of science is that it can be independently verified, and one of the fundamental qualities of hackers is that they don't typically trust "someone qualified" with "100s of millions of dollars" to do the verification when they can get a rough idea themselves. Hackers aren't here to let the "qualified" people just do their thing. We're here to learn, inspect, disassemble, discover, and most importantly, to create.

You're absolutely correct and I should have chosen my words more carefully.

So I'll change my words to say: I think it's sad that there are so many educated and capable people doing back of the envelope calculations on Hacker News. Half of us are capable of hunting down the original papers on solar towers and running the numbers through the proper calculations.

Also why are we just typing out the equations using text. It's the 21st century! We need a better way to discuss technical matters.

That is fair. I think you missed his subtle point though. For the person giving the millions it matters a lot if the numbers stuck up. For the hacker news bak of the envelope calculater estimates, round ups, even guesses suffice.

I think it is fair to say that while of course one should do the things you mentioned, one also would be wise to trust slightly more the "qulified" person, unless of course they want to go full blow on the matter and engage in thorough deep analysis.

Surely building the tower is going to offset a non-insignificant amount of it's CO2 'savings' vs Fossils?

Why does it have to be that tall ? is it because the top end becomes much cooler with more height ?

Looks like that is the case from the article..

For just $2trillion, we could build enough of these to supply power for 300m homes!

After I saw this story, I posted it to Facebook and my friend whose a journalist at Arizona's local news station picked it up and did a full blown story. http://www.azfamily.com/news/Massive-solar-tower-in-Arizona-...

The Empire State is New York State: http://en.wikipedia.org/wiki/Empire_State

Or did the article headline really mean the empire state BUILDING? http://en.wikipedia.org/wiki/Empire_State_Building

From the article:

"To put that in context - it will stand more than double the height of the Empire State building in New York City"

Lovely, downvotes. Guess we don't have too many New Yorkers in the readership here. FYI, you can't shorten the Chrysler Building to 'Chrysler' either. That's a corporation.

No, it's because you're splitting hairs when the message was obvious. They used 'height' not 'elevation', and it is common knowledge that the Empire State (Building) was once the tallest building in the world.

'building' is not optional.

Your burning karma thinks otherwise. Go find another hill to die on.

From http://ycombinator.com/newsguidelines.html :

Be civil. Don't say things you wouldn't say in a face to face conversation.

my username is 'awarzzkktsyfj'

Reply on news.ycombinator.com